Termination of rewriting under strategies

  • Authors:
  • Isabelle Gnaedig;Hélène Kirchner

  • Affiliations:
  • INRIA and LORIA, Vandoeuvre lès Nancy Cedex France;INRIA and LORIA, Vandoeuvre lès Nancy Cedex France

  • Venue:
  • ACM Transactions on Computational Logic (TOCL)
  • Year:
  • 2009

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Abstract

A termination proof method for rewriting under strategies, based on an explicit induction on the termination property, is presented and instantiated for the innermost, outermost, and local strategies. Rewriting trees are simulated by proof trees generated with an abstraction mechanism, narrowing and constraints representing sets of ground terms. Abstraction introduces variables to represent normal forms without computing them and to control the narrowing mechanism, well known to easily diverge. The induction ordering is not given a priori, but defined with ordering constraints, incrementally set during the proof. It is established that termination under strategy is equivalent to the construction of finite proof trees schematizing terminating rewriting trees. Sufficient effective conditions to ensure finiteness are studied and the method is illustrated on several examples for each specific strategy.